The invention disclosed herein pertains generally to sealing apparatus, and more particularly to an arrangement of pressure contoured, steam filled regions for sealing the shafts of turbines and the stems of valves.
A steam seal system of the type disclosed herein, wherein a third region is arranged between first and second regions to provide an equalizing region, and from which a mixture of steam and air is exhausted, is described in DEGbm No. 72 40 334.
A primary object of the present invention is to provide an improved steam seal apparatus for the shafts of turbines and the stems of valves, wherein a turbine is driven by contaminated steam.
A further object of the present invention is to provide a steam seal apparatus for a shaft of a turbine which includes safety features which will make it less likely that the steam seal apparatus will fail.
Apparatus for sealing the shafts of steam turbines and the stems of valves, according to a preferred embodiment of the present invention, includes a high pressure steam turbine and a low pressure steam turbine. The high pressure steam turbine receives steam produced in a nuclear reactor, which steam is generally contaminated, through a first line which includes a control valve. The contaminated steam exhausted from the high pressure turbine is fed to the low pressure turbine through a second line which includes a flap valve. A portion of a shaft of the high pressure steam turbine upstream from the turbine's blades, and a portion of the shaft of the high pressure steam turbine downstream from the turbine's blades are encircled by five sealing rings or glands and four sealing rings, respectively. The five rings are separated by four steam filled regions, i.e., each two adjacent rings are separated by a steam filled region, while the four sealing rings are separated by three steam filled regions. Similarly, upstream and downstream portions of a shaft of the low pressure steam turbine are each encircled by four sealing rings, which four sealing rings are separated by three steam filled regions. A stem of the control valve is encircled by five glands which are separated by four steam filled regions, while the flap valve includes four sealing glands which are separated by three steam filled regions.
The steam filling the regions between the turbine sealing rings and the valve sealing rings is either contaminated steam or relatively pure, uncontaminated steam. The contaminated steam is tapped from the line feeding contaminated steam to the high pressure steam turbine and is fed to selected steam regions by feedlines while the pure, uncontaminated steam is produced in a vaporizer and is fed to selected steam regions by different feed lines. In addition, pure and contaminated steam which flows out of, or leaks from, the selected steam regions is fed to other selected steam regions by still other feed lines.
The pressures of the steam in the various steam regions are set at levels which both produce a steam seal and produce predetermined leakoffs of steam and air. With respect to each of the turbine shafts, a pressure of the steam in a steam region farthest from the turbine is set below atmospheric pressure which results in an influx of air and a leakoff of steam and air. A pressure of the steam in a region closest to the turbine, which region receives contaminated steam, is higher than that in the region farthest from the turbine and higher than a condenser steam pressure, which results in a controlled leakoff of contaminated steam. A region situated between the abovementioned regions receives pure steam and exhibits a steam pressure above atmospheric pressure, which results in a controlled leakoff of pure steam.
The apparatus described above is advantageous because the regions which receive contaminated steam constitute a first steam seal system, system A, while the regions which receive pure steam constitute a second (and redundant) steam seal system, system B. While system B generally must operate properly to seal system A from the atmosphere, i.e. to prevent contaminated steam from being released to the atmosphere, either system alone can be operated to produce an effective steam seal, at least for short periods of time. Thus, if there is an unexpected cutoff in the supply of pure steam, the turbines can continue to operate without a loss of vacuum while a normal shutdown of the turbines is effected. If necessary, a normal shutdown of the nuclear reactor can also be effected because of the redundancy in the steam sealing apparatus.
The apparatus described above is also advantageous because the inflow of air produced by the below-atmospheric steam pressure in the regions furthest from each of the turbines results in an improved sealing effect.